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Decoding Galactic Merger Histories

1
Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA
2
Departamento de Física y Astronomía, Universidad de La Serena, La Serena 1720236, Chile
3
Vatican Observatory, Piazza Sabatini, 4B/5, 00041 Albano Laziale RM, Italy
4
Leibniz-Institut für Astrophysik Potsdam (AIP), 14482 Potsdam, Germany
5
Department of Astronomy, University of Washington, Seattle, WA 98195, USA
6
Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL 35487, USA
7
Department of Physics and Astronomy, University of Louisville, Louisville, KY 40292, USA
*
Author to whom correspondence should be addressed.
Galaxies 2017, 5(4), 95; https://doi.org/10.3390/galaxies5040095
Received: 30 June 2017 / Revised: 30 November 2017 / Accepted: 1 December 2017 / Published: 8 December 2017
(This article belongs to the Special Issue On the Origin (and Evolution) of Baryonic Galaxy Halos)
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Abstract

Galaxy mergers are expected to influence galaxy properties, yet measurements of individual merger histories are lacking. Models predict that merger histories can be measured using stellar halos and that these halos can be quantified using observations of resolved stars along their minor axis. Such observations reveal that Milky Way-mass galaxies have a wide range of stellar halo properties and show a correlation between their stellar halo masses and metallicities. This correlation agrees with merger-driven models where stellar halos are formed by satellite galaxy disruption. In these models, the largest accreted satellite dominates the stellar halo properties. Consequently, the observed diversity in the stellar halos of Milky Way-mass galaxies implies a large range in the masses of their largest merger partners. In particular, the Milky Way’s low mass halo implies an unusually quiet merger history. We used these measurements to seek predicted correlations between the bulge and central black hole (BH) mass and the mass of the largest merger partner. We found no significant correlations: while some galaxies with large bulges and BHs have large stellar halos and thus experienced a major or minor merger, half have small stellar halos and never experienced a significant merger event. These results indicate that bulge and BH growth is not solely driven by merger-related processes. View Full-Text
Keywords: galaxies: general; galaxies: evolution; galaxies: halos; galaxies: stellar content; galaxies: bulges; galaxies: merger history galaxies: general; galaxies: evolution; galaxies: halos; galaxies: stellar content; galaxies: bulges; galaxies: merger history
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Bell, E.F.; Monachesi, A.; D’Souza, R.; Harmsen, B.; De Jong, R.S.; Radburn-Smith, D.; Bailin, J.; Holwerda, B.W. Decoding Galactic Merger Histories. Galaxies 2017, 5, 95.

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